A sucker rod pumping unit reciprocates a rod string to actuate a subterranean pump for the purpose of lifting liquids to the surface. An exemplary embodiment is shown in FIG. 1. Such units are often instrumented with various sensors affixed to the pumping unit for the purpose of tracking pump and well performance. Historically, this instrumentation included sensors such as (but not limited to) rod load cell, crank position sensor, motor position sensor, motor current/voltage sensors, and beam inclinometer.
In addition to tracking system performance, these sensors can also be used to improve or optimize the pumping system operation, maximize production rates, and/or protect pumping equipment. For example, feedback information from sensors allows for the generation of “dynamometer plots” (pump load versus position data) which can be used to infer valuable down-hole conditions such as pump load, pump flow rate, well inflow, and pump health, which can in turn be used to improve or optimize the pumping system operation.
Sensors externally affixed to a pumping unit add additional cost, represent a potential failure mode, require frequent maintenance, and are often not functional owing to poor maintenance or neglect. Failure of these devices, especially in remotely located areas, can cause the pumping system to operate to sub-optimally, possibly hindering production rates and/or causing damage to the pumping system.
U.S. Pat. No. 7,168,924 describes a method whereby the rod load cell sensor may be eliminated, thus providing a less expensive and more reliable system. The '924 patent is assigned to the assignee of this application and is incorporated herein, in full, as if fully set-forth herein. However, a positioning sensor of some kind is still required for referencing of the absolute position of the pumping unit. This could include a crank position sensor (a discretely activated sensor or switch affixed to the pumping unit crank arm), an inclinometer affixed to the pumping unit main beam (Also referred to as a walking beam), or any other such method of determining crank position with an externally mounted “reference” device.
The apparatus of the present disclosure must also be of construction which is both durable and long lasting, and it should also require little or no maintenance to be provided by the user throughout its operating lifetime. In order to enhance the market appeal of the apparatus of the present disclosure, it should also be of inexpensive construction to thereby afford it the broadest possible market. Finally, it is also an objective that all of the aforesaid advantages and objectives be achieved without incurring any substantial relative disadvantage.